Question

On the basis of thermochemical equations (a),
(b) and (c), find out which of the algebric
relationships given in options (i) to (iv) is correct.
(1) C (graphite) + O₂(g) ⟶ CO₂(g);
△ᵣH = x kJ mol⁻¹
(2) C(graphite) + 1 O₂(g) ⟶ CO (g);
2
△ᵣH = y kJ mol⁻¹
(3) CO (g) + 1 O2 (g) ⟶ CO₂ (g);
2
△ᵣH = z kJ mol⁻¹
(a) z = x + y (b) x = y – z
(c) x = y + z (d) y = 2z – x

Answer 1

The algebraic  relationships given is (c) x = y + z

Explanation:

From question, the change in enthalpy due to formation of CO₂

Δf° H (CO₂) = x

From question, the change in enthalpy due to formation of CO

Δf° H (CO) = y

The change in enthalpy due to formation of reactant:

ΔrH = Δf° H (CO₂) - Δf° H (CO) - 1/2 Δf° H (O₂)

∵ 1/2 Δf° H (O₂) = 0

Now,

ΔrH = Δf° H (CO₂) - Δf° H (CO) - 0

∴ z = x - y